Note: Descriptions are shown in the official language in which they were submitted.
RADIOGRAPHIC ELEMENTS
WITH SELECTED CONTRAST RELATIONSHIPS
Field of the Di~closu~e
The invention relates to radiographic
imaging. More ~pecifically, the invention relates to
double coated silver halide radiographic elements of
the type employed in combination with intensifying
screens.
Background
In medical radiography an image of a
patient's tissue and bone structure i8 produced by
exposing the patient to ~-radiation and recording the
pattern of penetrating X-radiation using a
radiographic element containing at least one
radiation-sensitive silver halide emulsion layer
coated on a transparent ~usually blue tinted~ film
~upport. The X-radiation can be directly recorded by
the emulsion layer where only limited areas of
e~posure are required, as in dental imaging and the
imaging of body extremities. ~oweYer, a more
efficien~ approach, which greatly reduces X-radiation
exposures, is to employ an intensifying screen in
combination with the radiographic element. The
intensifying screen absorbs ~-radiation and emits
longer wavelength electromagnetic radiation which
~ilver halide emulsions more readily absorb. Another
technique for reducing patien~ exposure is to coat ~wo
silver halide emulsion layers on opposite sides of the
film support to form a "double coated" radiographic
element.
Diagnostic needs can be satis~ied at the
lowest patient X-radiation exposure levels by
employing a double coated xadiographic element in
combination with a pair of intensifying screens. The
æilver halide emulsion layer unit on each side of the
support directly absoxb~ about 1 to 2 percent of
incident X~radiation. The front screen, the screen
nearest the X-radiation source, absorb~ a much higher
percentage of X-radiation, but ~till tran~mits
sufficient X-radiation to expose the back screen, the
screen farthest from the X-radiation source. In the
overwhelming majority of application~ t~e front and
back ~creens are balanced ~o that each absorbs about
the same proportion of the total X-radiation.
However, a few variations have been reported from time
to time. A specific example of balancing front and
back ~creens to maximize image sharpness is provided
by Luckey et al U.S. Patent 4,710,637. Lyons et al
U.S. Patent 4,707,435 discloses in Example lO the
combination of two proprietary screens, Trimax ~TM
employed as a front screen and Trimax l~FTM employed
as a back æcreen. K. Rossman and G. Sanderson,
~Validity of the Modulation Transfer Function of
Radiographic Screen-Film Systems Measured by the Slit
Method~, Phys. Med. Biol., 1968, vol. 13, no. 2, pp.
259-268, report the use of unsymmetrical screen-~ilm
assemblies in which either the two screens had
measurably different optical characteristics or the
two emul~ions had measurably di~ferent optical
properties.
An imagewise exposed double coated
radiographic element contains a latent image in each
of the two silver halide emulsion units on opposite
sides of the film support. Proceæsing convert~ the
latent images to silver images and concurrently fixes
out undeveloped æilver halide, rendering the ~ilm
light insensitive. When the film is mounted on a view
box, the two superimposed silver images on opposite
sides of the support are ~een as a single image
against a white, illuminated background.
It has been a continuing objective of medical
radiography to maximize the information content of the
diagnostic image while minimizing patient expoæure to
X-radiation. In 1918 the Eastman Kodak Company
2~8~
introduced the first medical radiographic product that
was double coated, and the Patterson Screen Company
that same year introduced a matched intensifying
screen pair for that product.
An art recognized diffi~ulty wit~ employing
double coated radiographic elements in combination
with intensifying screens a~ described above i8 that
some light emitted by each ~creen passes through the
transparent film support to expose the silver halide
emulsion layer unit on the opposite side of the
support to light. The light emitted by a æcreen that
expo~es the emulsion layer unit on the opposite side
of the support reduces image sharpnes~. The effect i~
referred to in the art as crossoYer.
A variety of approaches have been suggested
to reduce crossover, a~ illustrated by Research
Disclosure, Vol. 184, August 1979, Item 18431, Section
V. Cross-Over Exposure Control. Research Disclosure
is published by Kenneth Mason Publications, Ltd.,
Dudley Anne2, 21a North Street, Emsworth, ~ampshire
PO10 7DQ, England. While some of these approaches are
capable of entirely eliminating crossover, they either
inter~ere with (typically entirely prevent) concurrent
viewing of the superimposed silver images on opposite
sides of the support as a ~ingle image, require
separation and tedious manual reregi~tration o~ the
æilver images in the course of eliminating the
crossover reduction medium, or significantly
desenæitize the silver halide emulsion. As a result,
none of these crossover reduction approaches have come
into common usage in the radiographic art. An example
of a recent crossover cure teaching of this type is
Bollen et al European published patent application
276,497, which interposes a reflective support between
the emulsion layer units during imaging.
The mo~t succegsful approach to crossover
reduction yet realized by the art consistent with
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viewing the ~uperimposed silver images through a
transparent film support without manual registration
of images haæ been to employ double coated
radiographic elements con~aining spectrally ~ensitized
5 high a~pect ratio tabular grain emul~ions or thin
intermediate aspect ratio tabular grain emul~ions,
illustrated by Abbot~ et al U.S. Patents 4,425,425 and
4,425,426, respectively. Wherea~ radiographic
elements typically exhibited crossover levels of at
lea~t 25 percent prior to Abbott et al, Abbott et al
provide examples of crossover reductions in the 15 to
22 percent range.
Still more recently Dickerson et al U.S.
Patent 4,803,150 has demonstrated that by combining
the teachings of Abbott et al with a processing
solution decolorizable microcrystalline dye located
between at least one of the emulsion layer units and
the transparent film support "zero" crossover levels
can be realized. Since the technique used to
determine crossover, single screen exposure of a
double coated radiographic element, cannot distinguish
between exposure of the emulsion layer unit on the
side of the support remote from the screen caused by
crossover and the exposure caused by direct absorption
of X-radiation, "zero" crossover radiographic elements
in reality embrace radiographic element~ with a
mea~uxed cros~over (including direct X-ray absorption)
of less than about 5 percent. Specific ~elections of
hydrophilic colloid coating coverage~ in the emulsion
and dye containing layers to allow the "zero~'
crossover radiographic elements to emerge dry to the
touch from a conventional rapid access processor in
less than 90 seconds with the cros~over reducing
microcrystAlline dye deolorized.
Although major improvements in radiographic
elements have occurred over the years, some
limitations have been heretofore accepted as being
inherent consequences of the complexitie~ of medical
diagnostic imaging. Medical diagnostic imaging places
extreme and varying demands on radiographic elements.
One o~ the most difficult demands can be illustrated
by the chest X-ray. In a typical chest X-ray the
radiologist is confronted with attempting to visually
detect both lung and ~eart anomalies, even though the
X-radiation absorption in the heart area is about 10
times greater than that of the lung area. Most double
coated radiographic elements when exposed to provide
an optimum contrast image of the lungs provide no
visually discernable contrast in the image of the
heart. This is because the radiographic element is
receiving in the heart area only about one tenth the
exposure it is receiving in the lung area. The art
has prior to this invention attempted to meet the
needs of radiologists for chest X-ray images providing
visually discernable features in both the heart and
lung image areas by providing extended latitude
radiographic elements. Extended latitude radiographic
elements are typically created by employing
polydispersed silver halide emulsions to provide lower
average contrasts and therefore a wider range of
exposures separating minimum and maximum density
exposures.
Su~m~ry of the Invention
In one aspect this invention is directed to a
radiographic element comprised of a transparent film
support, first and second silver halide emulsion layer
units coated on opposite sides of the film support,
and means for reducing to less than 10 percent
crossover of electromagnetic radiation of wavelengths
longer than 300 nm capable of ~orming a latent image
in t~e silver haiide emulsion layer units, ~aid
crossover reducing means being decolorized in less
than 90 seconds during processing of said emulsion
layer units.
The radiographic elements are characterized
in that the ~irst 6ilver halide emulsion layer unit
exhibits an average contra~ of less than 2.0, based
on density measurements at 0.25 and 2.0 above minimum
density and ~he second silver halide emul~ion layer
unit exhibits an average contrast of at lea~t 2.5,
based on density measurements at 0.25 and 2.0 above
minimum density. The contrast of the first ~ilver
halide emulsion layer unit i8 determined with t~e
fir~t silver halide emulsion unit replacing the second
silver halide emulsion unit to provide an arrangeme~t
with the flrst silver halide emul~ion unit present on
both sides of the tranparent cupport~ and the contrast
of the second silver halide emulsion layer unit is
determined with the second silver halide emulsion unit
replacing the first silver halide emulsion unit to
provide an arrangement with the second silver halide
emulsion layer unit present on both sides of the
tranparent support.
It is has been discovered that these double
coated radiographic elements are capable of yielding a
greater than 50 percent increase in contrast in heart
areas while providing the same contrast in lung area~
as conventional extended latitude double coated
radiographic element~. The invention therefore
repre3ents a significant advance in meeting the
diagno3tic needs of medical radiologists. Further,
while the advantages are discussed in terms of
simultaneously obtaining viæually useful imaging
detail in both heart and lung areas, it i~ appreciated
that the advantages of the invention extend to any
imaging application in which the X-radiation
absorption capabilities of the object be;ng examined
differ over a wide range.
Brief Descrie~ion of the Drawings
Figure 1 is a schematic diagram of an
assembly consisting of a double coated radiographic
element gandwiched between two intensi~ying screeng.
Description of preferred Embodiments
The double coated radiographic elements of
this invention o~fer the capability of producing
5 ~uperimposed ~ilver ;mage~ capable of transmis~ion
viewing which can satis~y the highest standards of the
art in terms of speed and sharpness. At the same time
the radiographic element6 are capable of providing
useful imaging detail over a wide range of exposuxe
levels within a 8 ingle image.
This is achieved by constructing the
radiographic element with a transparent film support
and first and second emulsion layer units coated on
opposite sides of the support. This allows
transmission viewing of the silver images on opposite
sides of the support after exposure and processing.
Between the emulsion layer units on opposite
sides of the support, means are provided for reducing
to less than 10 percent crossover of electromagnetic
radiation of wavelengths longer than 300 nm capable of
forming a latent image in the silver halide emulsion
layer unit~. In addition to having the capability of
absorbing longer wavelength radiation during imagewise
exposure of the emulsion layer units the crossover
reducing mean~ must also have the capability o~ being
decolorized in less than 90 seconds during processing,
so that no visual hindrance is presented to viewing
the ~uperimposed silver images.
The crossover reducing means reduces
crossover to less than 10 percent, preferably reduces
crossover to less than 5 percent, and optimally
reduces crossover to less than 3 percent. ~owever, it
must be kept in mind that for crossover measurement
convenience the crossover percent being referred to
also includes "false crossover", apparent crossover
that is actually the product of direct X-radiation
absorption. That is, even when crossover of longer
wavelength radia~ion i8 entirely elimi~ated, measured
cro~over will 8till be in ~he range of 1 to 2
percent, attributable to the ~-radiation that iB
directly ab80rbed by the emul~ion farthest ~rom the
intensi~ying screen. Crossover percentages are
determined by the procedures ~et forth in Abbott et al
U.S. Patents 4,425,425 and 4,425,426.
In addition to the above requirements, the
radiographic element~ o~ this invention differ from
conventional double coated radiographic elements in
requiring that the first and second emulsion layer
units exhibit significantly di~ferent average
contra3ts. The first silver halide emulsion layer
unit e~hibit~ an average contrast of le~s than 2.0
~hile the ~econd silver halide emulsion layer unit
e~hibit~ an average contrast of a~ lea~t 2.5. It i~
preferred that the average contrast~ of the first and
sEcond silver halide emulsion layer units differ by at
leaæt 1Ø While the best choice of average
differences between the first and ~econd emulsion
layer units can tiffer widely, depending up the the
application to be serYed, in mo~t in~tance~ the first
and ~econd emulsion layer units e~hibit an average
contrast di~ference in the range of from 0.5 to 3.5.
optimally from 1.0 to 2.S.
The first and second silver halide emul~ion
units can exhibit identical or differing speedæ.
, 3 ince the lower a~erage eontrast emulsion
layer unit iB normally relied upon to provide image
detail in areas receiving the least expoæure to
~-rad;ation, it i6 preferred that the lower average
contrast emulsion unit exhibit a ~peed which i~ at
least equal to that of the higher avera~e contrast
emul8ion layer unit. The lower average contrast
emulæion layer unit can exhibit speeds up to 10 times
greater than those of the h~gher average contraæt
emulsi~n layer unit. It i~ generally preferred that
_9_
lower average con~rast emulsion layer unit exhibit a
speed ranging from equal to to four time~ greater than
that of the higher average contra~t emulsio~ layer
unit.
Customarily 3ensitometric characterizations
of double coated radiographic elementR generate
characteristic (denæity VR. log exposure) curves that
are the product of two identical emulsion layer units,
one coated on each of the two sides of the transparent
support. Therefore, to keep contrast and other
sensitometric measurements (minimum density, Rpeed,
maximum density, etc.) as compatible with customary
practices as possible, the contrast and other
sensitometric characteristics of the fir~t silver
halide emulsion layer unit are determined with the
first silver halide emulsion unit replacing the second
silver halide emulsion unit to provide an arrangement
with the first silver halide emulsion unit present on
both sides of the tranparent 3upport. The contrast
and other sensitometric characteristics of the second
silver halide emulsion layer unit are ~imilarly
determined with the second silver halide emulsion unit
replacing the first silver halide emulsion unit to
provide an arrangement with the second silver halide
emulsion unit present on both ~ides of the tranparent
support.
As employed herein the term "average
contrast" is employed to indicate a contrast
determined by reference to an emul~ion layer unit
characteristic curve at a density of 0.25 above
minimum density and at a density of 2.0 above minimum
density. The average contrast i8 the density
d;fference, 1.75, divided by the log of the difference
in e~posure levels at two reference points on the
characteri~tic curve, where the exposure levels are
meter-candle~seconds. As herein employed all
references to photographic speed are underQtood to
~ o -
refer to comparisons of exposure levels at a reference
density of 1.0 above minimum den~ity. While the speed
and average contrast characteristic curve reference
points have been arbitrarily selected, the selection~
are typical of those employed in the art. For
nontypical characteristic curves (e.g., direct
positive imaging or unusual curve shapes) other
reference densitieG can be selected.
By reducing or eliminating crossover and
employing emulsion layer units differing in average
contrast and, optionally, speed, independent
radiographic records are formed in a single double
coated radiographic element that provide better
de~inition of exposure differences in areas differing
in their level of exposure by 10 times (1.0 log E,
where E is measured in meter-candle-seconds). A
difference of 1.0 log E i8 also referred to herein as
difference of 100 relative log e~posure units. For
example, a speed difference of 0.3 log E is a speed
difference of 30 log relative exposure units, with one
emulsion layer unit exhibiting a speed twice that of
the other.
The remaining features of the double coated
radiographic elements of this invention can take any
convenient conventional form. In a specifically
preferred form of the invention the advantages of (1)
tabular grain emulæions as disclosed by Abbott et al
U.S. Patents 4,4~5,425 and 4,425,426, cited above,
hereinafter referred to as T-GrainTM emulsions; (2)
sharpness levels attributable to crossover levels of
less than lO percent, (3) crossover reduction without
emulsion desensitization or residual stain, and (4)
the capability of rapid access processing, are
realized in addition to the advantages discussed above.
These additional advantages can be realiæed
by selecting the ~eatures of the double coated
radiographic element of this invention according to
LS~
the teachings of Dickerson et al U.S. Patent
4,803,150. The followi~g represente a ~pecific
preferred selection of features. Referring to Figure
1, in ~he assembly shown a radiographic element 100
according to this invention i8 positioned between a
pair of light emitting intensifying 8creen8 201 and
207. The radiographic element support is comprised of
a transparent radiographic support element 101,
typically blue tinted, capable of transmitting light
to which it is exposed and optionally, similarly
transmissive subbing units 103 and 105. On the first
and second opposed major faces 107 and 109 of the
support formed by the under layer units are crossover
reducing hydrophilic colloid layers 111 and 113,
respectively. Overlying the crossover reducing layers
111 and 113 are light recording latent image forming
silver halide emulsion layer units 115 and 117,
respectively. Each of the emulsion layer units is
formed of one or more hydrophilic colloid layers
including at lea3t one silver halide emulsion layer.
Overlying the emulsion layer units 115 and 117 are
optional hydrophilic colloid protective overcoat
layers 119 and 121, respectively. All of the
hydrophilic colloid layers are permeable to processing
solutions,
In use, the assembly is imagewise exposed to
X-radiation. The X-radiation is principally absorbed
by the intensifying screens 201 and 202, which
promptly emit light as a direct function of X-ray
expo~ure. Considering first the light emitted by
screen 201, the light recording latent image formin~ -
emulsion layer unit 115 is positioned adjacent this
screen to receive the light which it emits. Because
of the proximity of the screen 201 to the emulsîon
layer unit 115 only minimal light scattering occurs
before latent image forming absorption occur8 in this
layer unit. Hence light emission from screen 201
2~
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forms a sharp image in emulsion layer unit 115.
~ owever, not all of the light emitted by
screen 201 i~ absorbed within emul~ion layer unit
115. Thig remaining light, unless otherwise ab~orbed,
will reach the remote emulsion layer unit 117,
resulting in a highly unsharp image being formed in
th;s remote emulsion layer unit. Both cros80ver
reducing layers 111 and 113 are interposed between the
screen 201 and the remote emulsion layer unit and are
capable of intercepting and attenuating thi3 remaining
light. Both of these layers thereby contribute to
reducing crossover e~posure of emulsion layer unit 117
by the screen 201. In an exactly analogous manner the
screen 202 produces a sharp image in emulsion layer
unit 117, and the light absorbing layers 111 and 113
similarly reduce crossover exposure of the emulsion
layer unit 115 by the screen 2Q2.
Following exposure to produce a stored latent
image, the radiographic element 100 iæ removed from
association with the intensifying screens 210 and 202
and processed in a rapid access processor -that is, a
processor, such as an RP-X-OmatTM proceesor, which
is capable of producing a image bearing radiographic
element dry to the touch in less than 90 seconds.
Rapid access processors are illustrated by Barnes et
al U.S. Patent 3,545,971 and Akio et al publiæhed
European published patent application 248,390.
Since rapid access processors employed
commercia~ly vary in their specific processing cycles
and selections of processing ~olutions, the preferred
radiographic elements satisfying the requirements of
the present invention are specifically identified as
being those that are capable of emerging dry to the
touch when processed in 90 seconds according to the
following reference condition~:
development 24 seconds at 35C,
fixing 20 seconds at 35C,
washing 10 seconds at 35C, and
dryin~ 20 seconds at 65C,
where the remaining time i3 taken up in transport
between processing steps. The development step
employs the following developer:
Hydroquinone 30 g
l-Phenyl-3-pyrazolidone 1.5 g
KOH 21 g
~aHC03 7.5 g
K2S03 44.2 g
Na2S205 12.6 g
NaBr 35 g
5-Methylbenzotriazole 0.06g
Glutaraldehyde 4.9 g
Water to 1 liter at pH 10.0, and
the fixing step employs the following fixing
composition:
Ammonium thiosulfate, 60%260.0 g
Sodium bisulfite 180.0 g
Boric acid 25.0 g
Acetic acid 10.0 g
Aluminum sulfate 8.0 g
Water to 1 liter at pH 3.9 to 4.5.
The preferred radiographic elements of the
present invention make possible the unique combination
of advantages set forth above by employing (1~
substantially optimally spectrally sensitized tabular
grain emulsions in the emulsion layer unitæ to reach
low crossover levels while ashieving the high covering
power and other known advantages of tabular grain
emulsions, (2) one or more particulate dyes in the
interlayer units to further reduce crossover to less
than 10 percent without emulsion desensitization and
minimal or no residual dye stain, and (3~ hydrophilic
colloid swell and coverage levels compatible with
obtaining uniform coatings, rapid access processing,
and reduced or eliminated wet pressure sensitivity.
s~
Each of these feature~ of the invention i3 discus~ed
in more detail below:
Each under layer unit contains a processing
solution hydrophilic colloid and a particulate dye.
The total concentration o~ the microcrystalline dye in
both under layer units is sufficient to reduce the
crossover of the radiographic element below 10
percent. This can be achieved when the concentration
of the dye i8 chosen to impart to the structure
5eparating the emulsion layer units an optical density
of at lea~t 2.00 at the peak wavelength of screen
emission to which the emul~ion layer units are
responsive. Although the dye can be unequally
distributed between the two under layer units, it i6
pre~erred that each under layer unit contain
sufficient dye to raise the optical density of that
under layer unit to 1.00. Using the latter value as a
point of reference, since it is conventional practice
to employ intensifying screen-radiographic element
combinations in which the peak emulsion sensitivity
matches the peak light emission by the intensifying
screens, it follows that the dye also exhibits a
density of at least 1.00 at the wavelength of peak
emission of the intensifying screen. Since neither
screen emissions nor emulsion sensitivities are
confined to a single wavelength, it iB preferred to
choose particulate dyes, including combinations of
particulate dyes, capable of imparting a density of
1.00 or more over the entire spectral region of
significant sensitivity and emission. For radio
graphic elements to be used with blue emitting
intensifying screens, such as tho~e which employ
calcium tungstate or thulium activated lanthanum
oxybromide phosphoræ, it iB generally preferred that
the particulate dye be se~ected to produce an op~ical
density of at least 1.00 over the entire spectral
region of 400 to 500 nm. For radiographic elementR
2~ S~ -
-15-
intended to be used with green emitting intensifying
screens, such as those employing rare earth (e.g.,
terbium) activated gadolinium oxysulfide or o~yhalide
phosphors, it is preferred that the particulate dye
exhibit a density of at least 1.00 over the spectral
region of 450 to 550 nm. To the extent the wavelength
of emission of the screens or the sensitivities of the
emulsion layers are restricted, the spectral region
over which the particulate dye must also e~fectively
absorb light is correspondingly reduced.
While particulate dye optical densitieY of
1.00, chosen as described above, are effective to
reduce crossover to less than 10 percent, it is
specifically recognized that particulate dye densities
can be increased until radiographic element crossover
is effectively eliminated. For example, by increasing
the particulate dye concentration so that it imparts a
density of 2.0 to the radiographic element, crossover
is reduced to o~ly 1 percent.
Since there is a direct relationship between
the dye concentration and the optical density produced
for a given dye or dye combination, precise optical
density selections can be achieved by routine
selection procedures. Because dyes vary widely in
their extinction coefficients and absorption profiles,
it is recognized that the weight or even molar
concentrations of particulate dyes will ~ary from one
dye or dye combination selection to the next.
The ~ize of the dye particles is chosen to
facilitate coating and rapid decolorization of the
dye. In general smaller dye particles lend themselves
to more uniform coatings and more rapid decoloriza-
tion. The dye particles employed in all instances
have a mean diameter of less than 10.0 ~m and
preferably less than 1.0 ~m. There is no
theoretical limit on the minimum size~ the dye
particles can take. The dye particles can be most
2~ 5~
-~6-
conveniently formed by crystallization from solution
in ~izes ranging down to about 0.01 ~m or less.
Where the dyes are initially crystallized in the form
of partlcles larger than desired for use, conventional
techni~ues for achieving ~maller particle sizes can be
employed, ~uch as ball milling, roller milling, sand
milling, and the like.
An import-ant criterion in dye selection is
their ability to remain in particulate form in
hydrophilic colloid layers of radiographic elements.
While the hydrophilic colloids can take any of various
conventional forms, such as any of the forms set forth
in Research ~i~51Osure. Vol. 176, December 1978, Item
17643, Section IX, Vehicles and vehicle extenders, the
hydrophilic colloid layers are most commonly gelatin
and gelatin derivatives (e.g., acetylated or
phthalated gelatin). To achieve adequate coating
uniformity the hydrophilic colloid must be coated at a
layer coverage of at least 10 mg/dm2. Any
convenient higher coating coverage can be employed,
provided the total hydrophilic colloid coverage per
side of the radiographic element does not exceed that
compatible with rapid access processing. ~ydrophilic
colloids are typically coated as aqueous solutions in
the pH range of from about 5 to 6, most typically from
5.5 to 6.0, to form radiographic element layers. The
dyes which are selected for use in the practice of
this invention are those which are capable o~
remaining in particulate form at those pH levels in
aqueous solutions.
Dyes which by reason of their chromophoric
make up are inherently ionic, such as cyanine dyes, as
well as dye~ which contain substituents which are
ionically dissociated in the above-noted pH ranges of
coating may in individual instance6 be sufficiently
insoluble to satisfy the requirements of this
invention, but do not in general constitute preferred
-17-
classes o~ dyes for use in the practice o~ the
invention. For example, dyes with sulfonic acid
~ubstituent~ are normally too soluble to satisfy the
requirements o~ the invention. On the other hand,
nonionlc dyes with carboxylic acid groups (depending
in some instances on the specific ~ubstitution
location of the carboxylic acid group~ are in general
insoluble under aqueous acid coating condition~.
Specific dye selectione can be made from ~nown dye
characteristics or by ob~erving ~olubilities in the pH
range of from 5.5 to 6.0 at normal layer coating
temperatures -e.g., at a reference temperature of 40C.
Preferred particulate dyes are nonionic
polymethine dyes, which include the merocyanine,
oxonol, hemioxonol, ~tyryl, and arylidene dyes.
The merocyanine dyes include, joined by a
methine linkage, at least one basic heterocyclic
nucleus and at least one acidic nucleu~. The nuclei
can be joined by an even number or methine groups or
in so-called "zero methine" merocyanine dyes, the
methine linkage takes the form of a double bond
between methine groups incorporated in the nuclei.
Basic nuclei, such as azolium or azinium nuclei, for
example, include those derived from pyridinium,
quinolinium, isoquinolinium, oxazolium, pyrazolium,
pyrrolium, indolium, oxadiazolium, 3E- or lH-benzo-
indolium, pyrrolopyridinium, phenanthrothiazolium, and
- acenaphthothiazolium quaternary salts.
Exemplary of the basic heterocyclic nuclei
are those satisfying Formulae I and II.
(I)
_ z3_ _
=C - (L=L)q- N-R
(I~)
1- - Q~
-C=L- (L=L)q-N-R
-18-
where
Z repre~ents the element~ needed to
complete a cyclic nucleus derived from basic
heterocyclic nitrogen compounds such as oxazoline,
oxazole, benzoxazole, the naphthoxazoles ~e.g.,
naphth~2,1-d]oxazole, naphth[2,3 d]oxazole, and
naphth[l,2-d~oxazole), oxadiazol~, 2- or 4-pyridine,
2- or 4-quinoline, 1- or 3-isoquinoline, benzo-
quinoline, lH- or 3H-benzoindole, and pyrazole, which
nuclei may be substituted on the ring by one or more
of a wide variety of substituentæ euch as hydroxy, the
halogens (e.g., fluoro, chloro, bromo, and iodo),
alkyl groups or substituted alkyl groups (e.g.,
methyl, ethyl, propyl, isopropyl, butyl, octy~,
dodecyl, octadecyl, 2-hydroxyethyl, 2-cyanoethyl, and
trifluoromethyl), aryl groups or substituted aryl
groups (e.g., phenyl, l-naphthyl, 2-naphthyl,
3-carboxyphenyl, and 4-biphenylyl), aralkyl groups
(e.g., benæyl and phenethyl), alkoxy groups (e.g.,
methoxy, ethoxy, and isopropoxy), aryloxy groups
(e.g., phenoxy and l-naphthoxy), alkylthio groups
(e.g., methylthio and ethylthio), arylthio groups
(e.g., phenylthio, -tolylthio, and 2-naphthylthio),
methylenedioxy, cyano, 2-thienyl, styryl, amino or
substituted amino groups (e.g., anilino, dimethyl-
amino, diethylamino, and morpholino), acyl groups,
(e.g., formyl, acetyl, benzoyl, and benzenesulfonyl);
Q' represents the elements needed to complete
a cyclic nucleus deri~ed from basic heterocyclic
nitrogen compounds such as pyrrole, pyrazole,
inda201e, and pyrrolopyridine;
R represents alkyl groups, aryl group~,
alkenyl groups, or aralkyl groups, with or without
substituents, (e.g., carboxy, hydroxy, sulfo, alko~y,
sulfato, thiosulfato, phosphono, chloro, and bromo
substituents);
s~
-19-
L iS in each occurrence independently
selected to represent a substituted or unsubstituted
methine group -e.g., -CR8= grOupB, where R8
represent~ hydrogen when the methine group i8
unsubstituted and most commonly represent~ al~yl of
from 1 to 4 carbon atoms or phenyl when the methine
group i8 substituted; and
q is 0 or 1.
Merocyanine dyes link one of the basic
heterocyclic nuclei described above to an acidic keto
methylene nucleus through a methine linkage, where the
methine groups can take the form -CR8= de~cribed
above. The greater the number of the methine groups
linking nucleî in the polymethine dyes in general and
the merocyanine dyes in particular the longer the
absorption wavelengths of the dyeæ.
Merocyanine dyes link one of the basic
heterocyclic nuclei described above to an acidic keto
methylene nucleus through a methine linkage a3
described above. Exemplary acidic nuclei are those
which satisfy Formula III.
~III)
o
,11_
~ \G2
where
G represents an alkyl group or substituted
alkyl group, an aryl or substituted aryl group, an
aralkyl group, an alkoxy group, an aryloxy group, a
hydroxy group, an amino group, or a substituted amino
group, wherein exemplary substituents can take the
various forms noted in connection with Formulae VI and
VII;
G can represent any one of the groups listed
for Gl and in addition can represent a cyano group,
L5~
-20-
an alkyl, or arylsulfonyl group, or a group
repre~ented by -C-Gl, or G2 taken together with Gl
can represent the elements needed to complete a cyclic
acidic nucleu~ such as those derived from 2,4-oxazoli-
dinone (e.g., 3-ethyl-2,4-oxazolidindione),
2,4-thiazolidindione (e g., 3-methyl-2,4-thiazolidin-
dione), 2-thio-2,4-oxazolidindione (e.g., 3-phenyl-2-
thio-2,4-oxazolidindione), rhodanine, such as
3-ethylrhodanine, 3-phenylrhodanine, 3-(3-dimethyl-
aminopropyl)rhodanine, and 3-carboxymethylrhodanine,
hydantoin (e.g., 1,3-diethylhydantoin and 3-ethyl-1-
phenylhydantoin), 2-thiohydantoin (e.g., 1-ethyl-3-
phenyl-2-thiohydantoin, 3-heptyl-1-phenyl-2-thiohydan-
toin, and arylsulfonyl-2-thiohydantoin>, 2-pyrazolin-
5-one, such as 3-methyl-1-phenyl-2-pyrazolin-5-one and
3-methyl-1-(4-carboxyphenyl)-2-pyrazolin-5-one,
2-isoxazolin-5-one (e.g., 3-phenyl-2-isoxazolin-5-
one), 3,5-pyrazolidindione (e.g., 1,2-diethyl-3,5-
pyrazolidindione and 1,2-diphenyl-3,5-pyrazolidin-
dione), 1,3-indandione, 1,3-dioxane-4,6-dione,
1,3-cyclohexanedione, barbituric acid (e.g.,
l-ethylbarbituric acid and 1,3-diethylbarbituric
acid>, and 2-thiobarbituric acid (e.g., 1,3-diethyl-
2-thiobarbituric acid and 1,3-bis(2-methoxyethyl)-2-
thiobarbituric acid).
Useful hemioxonol dyes exhibit a keto
methylene nucleus as ~hown in Formula III and a
nucleus as shown in Formula IV.
(IV)
G3
- \~4
where
G3 and G4 may be the same or different and may
represent alkyl, substituted alkyl, aryl, substituted
8~5~
-21-
aryl, or aralkyl, as illustrated for R ring
substituents in Formula I or G3 and G4 taken
together complete a ring system derived from a cyclic
secondary amine, æuch as pyrrolidine, 3-pyxroline,
piperidine, piperazine (e.g., 4-methylpiperazine and
4-phenylpiperazine), morpholine, 1,2,3,4-tetrahydro-
quinoline, decahydroquinoline, 3-azabicyclo[3,2,2~no-
nane, indoline, azetidine, and hexahydroazepine.
Exemplary oxonol dyes exhibit two keto
methylene nuclei as shown in Form~la III joined
through one or higher uneven number of methine groups.
Useful arylidene dyes exhibit a keto
methylene nucleus as shown in Formula III and a
nucleus as shown in Formula V joined by a methine
linkage as described above containing one or a higher
uneven number of methine groups.
(V)
~ - ~ G4
where
G3 and G4 are as previously defined.
A specifically preferred class of oxonol dyes
for use in the practice of the invention are the
oxonol dyes disclosed in Factor and Diehl European
published patent application 299,435. These o~onol
dyes satisfy Formula VI.
~VI~
O O~I
2 \ _ / ~ \ - / 2
wherein
Rl and R2 each independently represent alkyl
of from 1 to 5 carbon atoms.
A apecifically preferred class of arylidene
dyes for use in the practice of the invention are the
arylidene dyes disclosed in Diehl and Factor European
published patent applications 274,723 and 2,94,461.
These arylidene dyes satisfy Formula VII.
(VII~
R3 5
_ t C~ 2 ; ~herein
A represents a substituted or unsubstituted
acidic nucleus having a carboxyphenyl or sulfonamido-
phenyl substituent æelected from the group consisting
of 2-pryazolin-5-onee free of any substituent bonded
thereto through a carboxyl group, rhodanines;
hydantoins; 2 thiohydantoins; 4-thiohydantoins;
2,4-oxazolidindiones; 2-thio-2,4-oxazolidindiones;
isoxazolinones; barbiturics; 2 thiobarbiturics and
indandiones;
R represents hydrogen, alkyl of l to 4 carbon
atoms or benzyl;
Rl and R2, each independently, repre~ents
alkyl or aryl; or taken together with R5, R6, N,
and the carbon atoms to which they are attached
represent the atoms needed to complete a julolidene
ring;
R3 represent~ H, alkyl or aryl;
R5 and R6, each independently, represents ~ or
R5 taken together with Rl; or R6 taken together
with R2 each may represent ~he atoms necessary to
complete a 5 or 6 membered ring; and
m ic O or l.
Oxazole and oxazoline pyrazolone merocyanine
particulate dyes are also contemplated. The
particulate dyes of Formula VIII are pre~entative.
-23-
(VIII)
o
(I3R ~ CH C~
R7
In .~ormula (I), Rl and R2 are each
independently substituted or unsubstituted alkyl or
substituted or unsubstituted aryl, or together
represent the a~oms necessary to complete a
substituted or unsubstituted 5- or 6-membered ring.
R3 and R4 each independently represents H,
substituted or unsubstituted alkyl, substituted or
unsubstituted aryl, C02H, or NHS02R6. R5 is
H, substituted or unsubstituted alkyl, substituted or
unsubstituted aryl, carboxylate (i.e., COOR where R
is substituted or unsubstituted alkyl), or
substituted or unsubstituted acyl, R6 and R7 are
each independently substituted or unsubstituted alkyl
or substituted or unsubstituted aryl, and n i8 1 or
2. ~8 is either æubstituted or unsubstituted
alkyl, or is part of a double bond between the xing
carbon atoms to which Rl and R2 are attached. At
least one of the aryl rings of the dye molecule must
have at least one substituent that is C02~ or
NHS02R6 .
Oxazole and oxazoline benzoylacetonitrile
merocyanine particulate dyes are also contemplated.
The particulate dyes of Formula IX are represehtative.
(IX)
R --I ,N~ ~ =CH--C~=C~ -- ~R
2 !
~3
-24-
In Formula IX, Rl, R2, R3, R4, R5,
and R6 may each be substituted or unsubstituted
alkyl or substituted or unsubstituted aryl,
pre~erably ~ubstituted or unsubstituted alkyl of 1 to
6 carbon atoms or ~ubstituted or unsubstituted aryl
of 6 to 12 carbon atoms. R7 may be sub~tituted or
unsubstituted alkyl of from 1 to 6 carbon atoms. The
alkyl or aryl groups may be substituted with any of a
number of substituents as is ~nown in the art, other
than those, such as 3ulfo substituents, that would
tend to increase the solubility of the dye so much as
to cause it to become soluble at coating p~'s.
Examples of useful substituents include halogen,
alko~y, ester groups, amido, acyl, and alkylamino.
Examples of alkyl groups include methyl, ethyl,
n-propyl, isopropyl, n-butyl, isobutyl, n-pentyl,
n-hexyl, or iæohexyl. Examples of aryl groups
include phenyl, naphthyl, anthracenyl, pyridyl, and
styryl.
Rl and R2 may also together represent the
atoms necessary to complete a substituted or
unsubstituted 5- or 6-membered ring, such as phenyl,
naphthyl, pyridyl, cyclohexyl, dihydronaphthyl, or
acenaphthyl. T~is ring may be substituted with
~ubstituents, other than thoee, ~uch as ~ulfo
substituents, that would tend to increase the
~olubility of the dye so much as to cause it to
become ~oluble at coating pH's. Examples of ueeful
~ubstituents include halogen, alkyl, alkoxy,
ester, amido, acyl, and alkylamino.
Useful bleachable particulate dyes can be
found among a wide range of cyanine, merocyanine,
oxonol, arylidene (i.e., merostyryl), anthraquinone,
triphenylmethine, azo, azomethine, and other dyes,
such as tho~e satisfying the criteria of Formula X.
(X)
[D-(A)y]~Xn
-25- .
where D is a chromophoric light-absorbing compound,
which may or may not comprise an aromatic ring if y
is not 0 and which comprises an aromatic ring if y i8
0, A is an aromatic ring bonded directly or
indirectly to D, X is a substituent, either on A or
on an aromatic ring portion of D, with an ionizable
proton, y is 0 to 4, and n is 1 to 7, where the dye
is substantially aqueous insoluble at a p~ of 6 or
below and substantially aqueouR soluble at a p~ of 8
or above.
Synthesis of the paxticulate dyes can be
achieved by procedures known in the art for the
synthesis of dyes of the same classes. For example,
those familiar with techniques for dye synthesis
disclosed in "The ~yanine Dyes and Related
Compounds", Frances Hamer, Interscience Publishers,
1964, could readily ~ynthesize the cyanine,
merocyanine, merostyryl, and other polymethine dyes.
The oxonol, anthraquinone, triphenylmethane, azo, and
a~omethine dyes are either known dyes or substituent
variants of known dyes of theæe classes and can be
synthesized by known or obvious variants of known
synthetic techniques forming dyes of these classes.
Examples of particulate bleachable dyes
useful in the practice of this invention include the
following:
2~
~26-
Table I
Trimethine Pyrazolone Cinnamylide~e Dyes
General Structure:
~2
0 ,l~ ~3
~ ~ ~c-c~=cE-cH=~ ~ 2
CH3 Rl~
Dye Rl R2 R3 ~-max ~-max (x 104)
(methanol)
1 CH3 H C02H 516 4.62
2 C~3C0 H C2H 573 5.56
C2Et H C02H 576 5.76
4 C~3 C2H H 5063.90
C02Et C02H H 5605.25
Table II
20Benzoylacetonitrile Merocyanine Dyes
General Structure:
I 0 CH CH
Rl/ ~r/ \~ CN
C 2H5
Dye Rl R2 ~-max ~-max (~ 104)
(methanol)
n C6~13S2NH CH3 445 7.32
7 C~3S2NH c3~7 446 7.86
8 CH~S02NH n--C6H13 447 7.6
9 H CH3 449 6.5
-27-
Table II-~
Arylidene Dye~
General Structure;
IJ ~,.~ ,NHS02Ph
(i-PrO2CC~2~2N-~ _ ~ CH \~ ~ ~
c~3
Dye R ~-max ~-max (x 104)
(methanol)
H 424 3.98
11 CH3 423 3.86
Table III
Benzoylacetonitrile Arylidene Dyes
General Structure:
2~ -~ -CH=/ \._ / 2
20 Dye Rl RZ R3 ~-max ~-max (x 104)
(methanol)
12 i-PrO2CCH2 i-PrO2CCH2 C3H7 426 3.5
13 C2H5 CF3CH202CCH2 CH3 439 4.27
i Pro2ccH2 i Pr02CCH3 C~3 420 4.2
2H5 CF3CH20~c~Hz C3~7 430 4.25
28-
Table IV
Pyrazolone Merocyanines Dyes
General Structure:
R3
~ =CH-C~ ./ ~ 3
Dye Rl R2 R3 R4 ~-max max (x 104)
(methanol)
16 C2H5 CH3 H C02H 450 7.4
17 C2~5 CH3 ~02H H 452 7.19
R3
18 I O ~-=CH-CH=CH-CH_ ~ ~ ~/ ~ 3
CH2CH3 CH3
~-ma~ 562 nm -max = 11.9 x 104
(methanol)
25.Table V
Barbituric Acid Merocyanines Dyes
General Structure:
30I~ 0~=CH-C~=/-N~o
Dye Rl R2 R3 ~-max ~-max (x 104)
(methanol)
19 CH2PhC02H C2H5 C2~5 442 10.70
~ ~ ~8~ 6
-29-
Table VI
Benzoxazole Benzoylacetonitrile Merocyanine Dyes
General Structure:
O~ .=~
~ ~o \ .= ./ ~ R3
10 Dye Rl R2 R3
- Et MeOEtS02NH
21 - Me MeS02NX
22 MeOEtS02NH Et MeOEtS02N~
23 MeOEtS02NH Et He~S02NH
24 MeS02NH MeOEt MeS02NH
- CH2PhCO~H PrSOzNE
26 MeS02NH MeOEt PrS02NH
27 MeOEtS02NH MeOEt PrS02NH
28 EtS02N~ Et MeS02NH
29 EtS02NH Me MeS02N~
MeOEtS02N~ MeOEt MeOEtS02NH
31 ~exS02NH MeOEt MeS02NH
32 MeOEtS02NH MeOFt HexS02NH
33 -- CH2PhC02~ MeS02NH
34 MeS02NH Me MeS02NH
C02H Me MeS02M~
36 C02H Me PrS02NH
37 EtOEtOE~S02NH Et MeS02N~
3S 38 EtOEtOEtS02NH Et PrS02NH
39 PrS02NE Et MeS02NH
--30--
PrS02N~Me MeS02NH
41 MeS02N~I Et EtS02N:EI
42 EtS02NHEt EtS02N~I
43 BuS02NHEt MeS02NH
44 BuS02NHEt C02~
BuS02N~I Me MeS02NH
10 46 MeS02NHEt ~uS02NH
Table VII
Mi s cellaneou~ Dyes
Dve
co2
15 47 $ ~ - ~ c~ c02~
~-max = 502 nm
-max = 5.47 x 104
4g CN 0
~ 0~ ~ C~=C e ~ ~ --NH C~2~ C~2~
0~
7 -
49 N~N
: I~ O
t
C02~
-31-
5 0 ~ --N--N~ 3
OH
~o\ ,1~
2C~3
10 51 NN N--N--~ --N2
I~ ,0~
CN
52 -- ~ T--CN
~I\
N~IS02 (CH2 >3C~3
CN
5 3 ~ t--CN
~ \
I~ ,0
NHS02C~3
Z~ 5~
-32-
C~ ,CH3 CN
54 .~ ~0
Y 't~ \CN
l CN
I~ O
f
~SO2C~3
lo , - ~ ,
55 ~ -CH=~
~_ r c~3
~-max = 500 nm
~-max = 5 . 82 x 104
Table VIII
Arylidene Dyes
General Structure:
_ 0 3
\C=CH( C .~oj~
(HOOC)x C~ 4 n \.=./ ~ 2
l-Ph
1 2 3 4 Substn. x~-maX ~-max
Dye R ~ R R R Position n (nm2 (10 ~
56 C~3 HCE3 1 4 0 466 3.73
57 C2~5 ~CH3 1 4 0 471 4. 75
58 n-C4H9 HCH3 1 4 0 475 4.50
59 CH3 HCOOC2H5 1 4 0 508 5.20
60 i-C3R70C $ 2 C~3 CH3 1 4 0 430 3.34
61 C~3 ~ CH3 2 3 ~ 5 0 457 3.78
62 C2~5 H CH3 2 3 ~ 5 0 475 4. 55
63 n-C4~9 H CH3 2 3,5 0 477 4.92
-33-
64 i-C3~70C~ 2 ~H3 2 3,5 0 420 3.62
65 i-C3H70C~ 2 C~3 CH3 2 3,5 0 434 3.25
66 i-C3H70CCH2 H CH3 1 4 0 420 3.g4
67 CH3 H eCH3 1 4 1 573 5.56
68 CH3 ~ COOEt l 3,5 0 502 4.83
69 C2~5 ~ COOEt 1 4 0 512 6.22
70 CH3 H CF3 l 4 0 507 4.58
71 GH3 H Ph 1 4 0 477 4.54
72 CH3 H eCH3 1 4 0 S06 5.36
Table IX
Oxazole and Oxazoline Pyrazolone Merocyanine Dyes
C~3\ ~0 \ / ~ ~C02H
C 3 ~ c~3 \C02H
CH3
25 74
=CH-CH=~ -CO H
C 3
c~3
0
I O \-=CH-CH= / ~
C02H~
C~5
Z6~
34-
76 0
O~ U~
ClH2
I~ ,0
C02H
77I~`11'\ ~ /O-C2~
~ / ~/ C~2CH2CH3
CE~2CH3
o
78 I~`D \ ~-1 U~ co2~
c~2c~3
79 ~ /2
CH CH
2 3
~\ /\ ~ O co2~
c~2c~3
Z~ 6
--35--
81 0 U~l 'II-CO28
C~,C~3 ~./
82 CH3~ ~\ /O--t L~ C2
C~3~/ CO2CH2CH3 CO2H
o
83 CN3~0\ ~^=I `~I~ ~0--NESO2CH3
C~3~ CS2CH2CH3
CH3
0
84 1~`0,~
2 5 CH3
0 11 ~-~
I~0,~ ' 'CO H
\ ~ \
I~..,O~
2~
-36-
86 ~ \ ~ co~l~
I~;,û
co2
87
~3C\~/\ /~ t~ ,O-CO2H
3 \~ ., NH2
~- CC)2H
88 ~3C~ ~0~ ~ -CO2H
H3C ~ \C~3
I~o~
89
3C, 0~ ,.--~ NHS02-
I~ ,0~
-37-
so IJ
CH3~ /\ ~ g-N~S02C~3
O =- = o
~3\~' C~3
I O
~- C02H
91
\ ~ ,O-CO2H
I O ,~
~o2c/ ~c~ y I O
CH3 ~.,
92 8 ~ ~ ~C2E
~.~ ,o\ ,=, ~ ~
O s/ ,I
20 2 YC~3 I~,O co2~
~,
.. o
~10 C/~ y/-=- C~3--
C~3
O
94 IJ ~
30I~ '\ ~-t' ~ ~
CH3 5 2HN/ ~/ CH
CH2CH3 3
s~
--38--
U ~-
I~-`0'\.
C~I3S02~IN/ \~/ C62C~2CH3
~ C02H
1096
I~ 11' \t=~ NHso2 ~
CH3S02HN/ ~ / C~ ~ /
~ \CO H
97
20 CH3 C~ o=~
~/ \C02H
0
98 o
3 C~ \~/; =-
I O
:: ~./ \CQ2
~ f~5
-39
99
I~\ ~=I' ~ NHS02~ `o
53 C~3~ ~ CÉ3
I O
C02H
Table X
Oxazole and Oxazoline Benzoylacetonitrile
Merocyanine Dyes
100 O ~
C02H~- ~ CN
C~3
20 I~s `D' \.=c~ c~=C~C~ ~ - ~ ~C2~
C2H5
C~3\ / \ ~C~ -N~SO CH
102 ~ =CH-CE=C\ o=- 3
CH~3 ~ CN
CEI
~1
,0
t
C02H
`-- --
-40
CH3\ ,0~ ~ ~9 ~
1030 o=C~I-C~=C/ ~ 2 3 7
C~3~ CN
~lH2
I~t,O
10C02H
104 ~., ,0~ ll~ --C2CE2CH3
15H02C/ ~./ \~/
~ ~ \
I ~
~- C02H
105 . o ,ll~ --C2H
=' \CN
H02C/ ~./ \~/
11
~- C02H
106 I~ I~ O \-=-' \CN
30~-/ ~-/ \N/
I ,O
~. ~co
107~o\ /o\ U~ NHS02CH2C~3
CH 0/ ~ / ~/
\co ~
SOZC~2C32C33
~ ~O
~./ \C02~
Fl3,1 ~ ,0~ .=./ ~ N~502(C}~Z)3C~3
1, ~5.,
110 I~s ~ ~ .=./ ---~ N~SOzC~3
I~
~ C02H
111 C1~3~ 8_ ~ ~ co2~
0 =~ CN
c~3
c~3
~8~5~i
-42-
,0 ~ ,. =~ NHS02CE13
CH3 ~ /=- CN
I O
`co ~
113 8_. `.
,o\ .=,
3~/
\ ~ \
~ co H
114/o\ ~=c/ ~ _ ~ C2H
2 0
t~ ,~
~ \ /\ .=./ ~ NHS02C~2CH3
,I~ /O,N,-=~ \CN
30 CH2CEI3
116 C~3~ /\ ~~ C02H
O ~ CN
C~3\N/
CH2CH~CH3
o . -
117 CH o U--~ C2H
C~3\N~
CH2CH3
118 . 0 U_9~ ~._CO2
CH30 9 \N/
CH3
119 I~ `D \ = ' = 'c~ 2
2 0 CH3
120 ~., ,O\ U--~ C02H
./ ~o/ \N/
I~ ,D IH3
121 '-~ ll
t~ CN
C~3
2~8'~5~
-44-
122 ~ \ ~o=~ C2~
\~ CH
123 o /8.~ C02H
CH3CH2S02N~/ '' \N/ ,
C~12CH3
124 ~-\ /0 \ J-~ -NHS02CH3
CH3 ( C~2 ) 2 S 0 2N~
I~ ,0~
Table XI
Oxonol Dyes
8 1~
02C \ _ /~ =CE-CH=C~ CO H
R2
wherein
Dye R R2
125 CH3 C~3
126 C2H5 C2H5
The dye can be added directly to the
hydrophilic colloid as a particulate solid or can be
converted to a particulate solid after it i8 added to
the hydrophilic colloid. One example of the latter
technique is to dissolve a dye which is not water
-45-
soluble in a solvent which is water ~oluble. When the
dye solution i8 mixed with an aqueous hydrophilic
colloid, followed by noodling and washing of the
hydrophilic colloid (see ~esear~h ~i~closure, Item
17643, cited above, Section II), the dye solvent is
removed, leaving par~iculate dye dispersed within the
hydrophilic colloid. Thus, any water insoluble dye
which that i8 soluble in a water mi~cible organic
301vent can be employed as a particulate dye in the
lQ practice o~ the invention, provided the dye is
su3ceptible to bleaching under processing condi-
tions - e.g., at alkaline pH levels. Specific examples
of contemplated water miscible organic solvents are
methanol, ethyl acetate, cyclohexanone, methyl ethyl
ketone, 2-(2-butoxyethoxy)ethyl acetate, triethyl
phosphate, methylacetate, acetone, ethanol, and
dimethylformamide. Dyes preferred for use with these
solvents are sulfonamide substituted arylidene dyes,
specifically preferred examples of which are set forth
about in Tables IIA and III.
In addition to being present in particulate
form and satisfyin~ the optical density requirements
set forth above, the dyes employed in the under layer
units must be substantially decolorized on
processing. The term "substantially decolorized~ is
employed to mean that the dye in the under layer units
raises the minimum density of the radiographic element
when fully proeessed under the reference proces~ing
conditions, ~tated above, by no more than 0.1,
preferably no more than 0.05, within the visible
spectrum. As shown in the examples below the
preferred particulate dyes produce no signi~icant
increase in the optical density of fully processed
radiographic elements of the invention.
As indicated above, it is specifically
contemplated to employ a W absorber, preferably
blended with the dye in each of crossover reducing
-46-
layers 111 and 113. Any conventional W absorber can
be employed for thi~ purpose. Illu~trative u~eful W
absorber~ are those disclosed in Reseaxch Di~clo~u~e.
Item 18431, cited above, Section V, or Resea~ch
~i~5~103ure, Item 17643, cited abowe, Section VIII(C).
Pre~erred W absorbers are ~hose which either exhibi~
minimal absorption in the visible portion of the
spectrum or are decolorized on processing ~imilarly as
the crossover reducing dyes.
Overlying the under layer unit on each major
surface of the support is at lea~t one additional
hydrophilic colloid layer, specifically at one halide
emulsion layer unit comprised of a ~pectrally
sensitized silver bromide or bromoiodide tabular grain
emulsion layer. At least 50 percent ~preferably at
least 70 percent and op~imally at least 90 percent) of
the total grain projected area of the tabular grain
emulsion is accounted for by tabular grains having a
thickness less than 0.3 ~m (preferably less than 0. 7
~m) and an average aspect ratio of ~reater than 5:1
(preferably greater than 8:1 and optimally at least
12:1). Preferred tabular grain silver bromide and
bromoiodide emulsions are thoQe disclosed by Wilgus et
al U.S. Patent 4,434,226; Kofron et al U.S. Patent
4,439,530; Abbott et al U.S. Patents 4,4~5,425 and
4,425,426; Dickerson U.S. Patent 4,414,304; Maska~ky
U.S. Patent 4,425,501; and Dickerson U.S. Patent
4,5~0,098.
Both for purposes of achieving maximum
imaging speed and minimizing crossover the tabular
grain emulsions are substantially optimally spectrally
~ensitized. That is, sufficient æpectral sensitizing
dye is adsorbed to the emulsion grain surfaces to
achieve at least 60 percent of the maximum speed
attainable from the emulsions under the contemplated
conditions of exposure. It is known that optimum
spectral sensitization i8 achieved at about 25 to 100
-47-
percent or more o~ monolayer coverage of the total
available surface area presented by the grain~. The
preferred dyes for spectral senæitization are
polymethine dyes, such as cyanine, merocyaninet
hemicyanine, hemioxonol, and merostyryl dyes.
Specific examples of spectral sensitizing dyes and
their use to sen~itize tabular grain emulsions are
provided by Kofron et al U.S. Patent 4,439,520.
Although not a required feature of the
invention, the tabular grain emulsions are rarely put
to practical uæe without chemical sensitization. Any
convenient chemical sensitization of the tabular grain
emulsions can be undertaken. The tabular grain
emulsions are preferably substantially optimally (as
defined above) chemically and spectrally sensitized.
Useful chemical sensitizations, including noble metal
(e.g., gold) and chalcogen (e.g., sulfur and/or
selenium) sensitizations as well as selected site
epi~axial sensitizations, are disclosed by the patents
cited above relating to tabular grain emulsions,
particularly Kofron et al and Maskasky.
In addition to the grains and spectral
sensitizing dye the emulsion layers can include as
vehicles any one or combination of various
conventional hardenable hydrophilic colloids alone or
in combination with vehicle extenders, such as latices
and the like. The vehicles and vehicle extenders of
the emulsion layer units can be identical to those of
the interlayer units. The vehicles and vehicle
extenders can be selected from among those disclosed
by Re3ear~h Disclosure, Item 17643, cited above,
Section IX. Specifically preferred hydrophilic
colloids are gelatin and gelatin derivatives.
The coating coverages of the emulsion layers
3S are chosen to provide on processing the desired
maximum density levels. For radiography maximum
denRity levels are generally in the range of from
~8
~ 48-
about 3 to 4, although specific applications can call
for higher or lower density levels. Since the silver
images produced on opposite sides of the support are
~uperimposed during viewing, the optical density
observed is the sum of the optical densities provided
by each emulsion layer unit. Assuming equal #ilver
coverages on opposite major surfaces o~ the support,
each emulsion layer unit ~hould contain a sil~er
coverage from about 18 to 30 mg/dm2, preferably 21
to 27 mg/dm .
It ls conventional practice to protect the
emulsion layers from damage by providing overcoat
layers. The overcoat layers can be formed of the same
vehicles and vehicle extenders disclosed above in
~5 connection with the emulsion layers. The overcoat
layers are most commonly gelatin or a gelatin
derivative.
To avoid wet pressure sensitivity the total
hydrophilic colloid coverage on each major surface of
the support must be at least 35 mg/dm2. It i8 an
observation of this invention that it is the total
hydrophilic colloid coverage on each surface of the
support and not, as has been generally believed,
simply the hydrophilic colloid coverage in each silver
halide emulsion layer that controls its wet pressure
sensitivity. Thus, with 10 mg/dm2 of hydrophilic
colloid being required in the interlayer unit for
coating uni~ormity, the emulsion layer can contain as
little as 20 mg/dm2 of hydrophilic colloid.
To allow rapid access processing of the
radiographic element the total hydrophilic coating
coverage on each major surface of the support must be
less than 65 mg/dm , preferably less than 55
mg/dm2, and the hydrophilic colloid layers must be
~ubstantially fully forehardened. By substantially
fully ~orehardened it is meant that the processing
solution permeable hydrophilic colloid layers are
2 0 ~8
-49-
forehardened in an amount ~ufficient to reduce
swelling of these layers to less than 300 percent,
percent swelling being determined by the following
reference 3well determination procedure: (a)
incubating 3aid radiographic element at 38C for 3
days at 50 percent relative humidity, (b) meaeuring
layer thickness, (c) immersing ~aid radiographic
element in distilled water at 21C for 3 minutes, and
(d) determining the percent change in layer thickness
as compared to the layer thicknes~ measured in step
(b). This reference procedure for measuring
forehardening is disclosed by Dickerson U.S. Patent
4,414,304. Employing this reference procedure, it is
preferred that the hydrophilic colloid layers be
sufficiently forehardened that swelling i~ reduced to
le3s than 200 percent under the stated test conditions.
Any conventional transparent radiographic
element support can be employed. Transparent ~ilm
supports, such as any of those dieclosed in Research
Disclosure, Item 17643, cited above, Section XIV, are
all contemplated. Due to their superior dimensional
stability the transparent film supports preferred are
polyester supports. Poly(ethylene terephthalate) is a
specifically preferred polyester film support. The
support is typically tinted blue to aid in the
examination of image patterns. Blue anthracene dyes
are typically employed for this purpo~e. In addition
to the film itself, the support is usually formed with
a subbing layer on the major surface intended to
receive the under layer units. For further details of
support construction, including exemplary incorporated
anthracene dyes and subbing layers, refer to Research
Disclosure, Item 18431, cited above, Section XII.
In addition to the features of the
radiographic elements o~ this invention set forth
above, it i~ recognized that the radiographic elements
can and in most practical application3 will contain
5~
--50-
additional conventional feature3. Referring to
Re$ç~rch DisclQ~ure, Item 18431, ci~ed above, the
emulsion layer units can contain 8tabilizers,
antifoggants, and antikinking agents of the type ~et
forth in Section II, and the overcoat layers can
contain any of variety of conventional addenda of the
type set forth in Section IV. The outermost layers of
the radiographic element can al80 contain matting
agents of the type set out in Resear.ch Disclosure,
Item 17643, cited above, Section XVI. Referring
further to Research Disclosu~re, Item 17643,
incorporation of the coating aids of Section XI, the
plasticizers and lubricants of Section XII, and the
antistatic layers of Section XIII, are each
contemplated.
am~les
The invention can be better appreciated by
reference to the following specific examples:
S~reens
The following intensifying screens were
employed:
Sc~een X
This screèn has a composition and structure
corresponding to that of a commercial, general purpose
screen. It consists of a terbium activated gadolinium
oxysulfide phosphor having a median particle size of 7
~m coated on a white pigmented polyester support in
a PermuthaneTM polyurethane binder at a total
phosphor coverage of 7.0 g/dm2 at a phosphor to
binder ratio of 15:1.
Screen Y
This screen has a composition and structure
corresponding to that of a commercial, medium
resolution screen. It consists of a terbium activated
gadolinium oxysulfide phosphor having a median
particle size of 7 ~m coated on a white pigmented
polyester support in a PermuthaneTM polyurethane
2 ~ 6
~ 51-
binder at a total phosphor coverage of 5.9 g/dm2 at
a phosphor to binder ratio of 15:1 and containing
0 ~ 017535~/o by weight of a lOO:l weight ratio of a
yellow dye and carbon.
Scre~n Z
This screen has a composition and ~tructure
corresponding to that of a co~mercial, high resolution
screen. It consists of a terbium activated gadolinium
oxysulfide phosphor having a median particle size of 5
~m coated on a blue tinted clear polyester support
in a PermuthaneTM polyurethane binder at a total
phosphor coverage of 3.4 g/dm2 at a phosphor to
binder ratio of 21:1 and containing 0.0015% carbon.
Ra~i~graphic ~xI~sures
Assemblies consisting of a double coated
radiographic element sandwiched between a pair of
intensifying screens were in each instance e~posed as
follow~:
The assemblies were expo3ed to 70 KVp
X-radiation, varying either current (mA) or time,
using a 3-phase Picker Medical (Model VTX-650)TM
X-ray unit containing filtration up to 3 mm of
aluminum. Sensitometric gradations in exposure were
achieved by using a 21-increment ~0.1 log E) aluminum
step wedge of varying thickness.
~lement A ~example) (Em.LC~L~OA(Em.~C~
Radiographic element A was a double coated
radiographic element exhibiting near zero crossover.
Radiographic element A was constructed of a
low cros~over support composite (LXO) consisting of a
blue-tinted transparent polyester film support coated
on each æide with a crossover reducing layer
conslsting of gelatin (1.6g/m2) containing 320
mg/m o~ a 1:1 weight ratio mixture of Dyes 56 and
59.
Low contrast (LC~ and high contrast (HC)
emulsion layers were coated on opposite sides of the
52-
support over the crossover reducing layers. Both
emulsions were green-sensitized high aspect ratio
tabular grain silver bromide emul~ions, where the term
~high aspect ratio" is employed a~ defined by Abbott
et al U.S. Patent 4,425,425 to require that at least
50 percent of the total grain projected area be
accounted for by tabular grains having a thickness of
le~s than 0.3 ~m and having an average aspect ratio
of greater than 8:1. The low contrast emulsion was a
1:1 (silver ratio) blend of a firæt emulsion which
exhibited an average grain diameter of 3.0 ~m and an
average grain thickness of 0.13 ~m and a second
emulsion which exhibited an average grain diameter of
1.2 ~m and an average grain thickness of 0.13 ~m.
The high contrast emulsion exhibited an average grain
diameter of 1.7 ~m and an average grain thickness of
0.13 ~m. The high contrast emulsion exhibited less
polydispersity than the low contrast emulsion. Both
the high and low contrast emulsions were spectrally
sensitized with 400 mg/Ag mol of anhydro-5,5-dichloro-
9-ethyl-3,3'-bis(3-sulfopropyl)oxacarbocyanine
hydroxide, followed by 300 mg/Ag mol of potassium
iodide. The emulsion layers were each coated with a
silver coverage of 2.42 g/m and a gelatin coverage
of 3.22 g/m2. Protective gelatin layers (0.69
g/m2) were coated over the emulsion layers. Each of
the gelatin containing layers were hardened with
bis(vinylsulfonylmethyl) ether at 1% of the total
gelatin.
When coated as described above, but
symmetrically, with Emulsion LC coated on both sides
of the support and Emulsion HC omitted, using a Screen
X pair, Emulsion LC exhibited a relative log speed of
98 and an a~erage contrast of 1.8. Similarly,
Emulsion HC when coated æymmetrically with Emulsion LC
omitted exhibited a relative log speed of 85 and an
average contrast of 3Ø The emulæion~ thus differed
-53-
in average contrast by 1.2 while differing in speed by
13 relative log ~peed units (or 0.13 log E).
When Element A was tested for crossover as
described by Abbott et al U.S. Patent 4,425,425, it
exhibited a crossover of 2%.
Element B (control2 (Em. L~XOB(Em. L~
Radiographic element B was a conventional
double coated radiographic element exhibiting extended
exposure latitude.
Radiographic element B was constructed of a
blue-tinted transparent polyester film support lacking
the crossover reducing layers of radiographic element
A. Identical emulsion layers ~L) were coated on
opposite sides of the support. The emulsion employed
wa a green-sensitized polydisper3ed silver
bromoiodide emulsion. The same spectral sensitizing
dye was employed as in Element A, but only 42 mg/Ag
mole was required, since the emulsion was not a high
aspect ratio tabular grain emulsion and therefore
required much less dye for substantially optimum
sensitization. Each emulsion layer was coated to
provide a silver coverage of 2.62 g/m2 and a gelatin
coverage of 2.85 g/m . Protective gelatin layers
(0.70 g/m2) were coated over the emulsion layers.
Each of the layeræ were hardened with
bis(vinylsulfonylmethyl) ether at 0.5% of the total
gelatin.
. When coated as described above, using a
Screen X pair, the film exhibited a relative log E
speed of 80 and an average contrast of 1.6.
When Element B was tested for crossover as
described by Abbott et al U.S. Patent 4~425,425, it
exhibi~ed a crossover of 25~/o.
~lement C (cont~ol~ (Em.MC)~OC(Em.MC)
Radiographic element C was a conven~ional
double coated radiographic element of a type employed
on occasion for chest cavity examinations.
-54-
Radiographic element C was constructed like
radiographic element B, excep~ that medium contrast
emulsion layers (MC~ were employed and the ~ilver
coverage of each emulsion layer was reduced to 1.93
glm .
When coated as described above, using a
Screen X pair, the film exhibited a relative log E
speed of 80 and an average con$rast of 2.6.
When Element C was tested for crosæover as
described by Abbott et al U.S. Patent 4,425,425, it
exhibited a crossover of 30%.
lem~nt D (control) (Em.HC)HXOD(Em.~C)
Radiographic element D was a conventional
high aspect ratio tabular grain double coated
radiographic element of a type employed on occasion
for chest examinations of subject~ having low chest
densities -i.e., children or adults of slight build.
Radiographic element D was constructed like
radiographic element A, except that no crossover
reducing layers were coated on the film support and a
high contrast emulsion (HC) similar to that employed
in radiographic element A was coated on both sides of
the ~upport.
When coated as described above, using a
Screen X pair, the film e~hibited a relative log E
speed of 80 and an average contrast of 2.9.
When Element C was tested for crossover as
deæcribed by Abbott et al U.S. Patent 4,425,425, it
exhibited a crossover of 20%.
Processing
The films were processed in 90 seconds in a
commercially available Kodak RP X-Omat (Model 6B)TM
rapid accese processor as follows:
development 20 seconds at 35C,
fixing 12 seconds at 35C,
washing 8 Qeconds at 35DC, and
drying 20 ~econds at 65~C,
~ 5
-55-
where the remaining time is taken up in transport
between processing steps. The development step
employs the following develope~:
~ydroquinone 30 g
1-Phenyl-3-pyrazolidone 1.5 g
KOH ~1 g
Na~C03 7 5 g
K2S03 44.2 g
Na2S205 12.6 g
NaBr 35 g
5-Methylbenzotriazole 0.06g
Glutaraldehyde 4.9 g
Water to 1 liter at pH 10.0, and
the fixing step employs the ~ollowing fixing
composition:
Ammonium thiosulfate, 60~/o260 ~ O g
Sodium bisulfite 180.0 g
Boric acid 25.0 g
Acetic acid 10.0 g
Aluminum sulfate 8.0 g
Water to 1 liter at pH 3.9 to 4.5.
Sensitometry
Optical densities are expressed in terms of
diffuse density as measured by an X-rite MOdel 310
densitometer, which was calibrated to ANSI standard P~
2.19 and was traceable to a National Bureau of
Standards calibration step tablet. The characteristic
curve (density vs. log E) was plotted for each
radiographic element processed. The average gradient,
presented in Table XII below under the heading
Contrast, was determined from the characteristic curve
at den~ities of 0.25 and 2.0 above minimum density.
Assemblies
Two assemblies were formed by placing
Element A (satisfylng the reguirement~ of the
invention~ and each of the control elements, Elements
B, C, and D, between a pair of intensifying screens as
200B~15fi
..
. .
-56-
indicated in Table XII.
Table XII
Contrast
Sc~een/Film Ass~mbly Average Ll~eg ~ea~t
5 I. Z(Em.LC)LXOA(Em.~C)X 1.5 100 100 (Example)
II. Z(Em. L)~XOB(Em. L~X 1.6 100 ~0 (Control)
III.X(Em. L)~XOB(Em. L)Z 1.6 100 60 (Control)
IV. X(Em. L)~XOB(Em. L)X 1.6 100 60 (Control)
V. Z(Em.MC)HXOC(Em.MC~Z 2.6 115 20 (Control)
10 VI. Z(Em.HC)HXOD(Em.~C)Z 2.9 130 20 (Control)
VII. Z(Em.FLC)L~OE(Em.SHC)X 2.5 115 40 (Example)
VIII.Z(Em.S~C)LXOE(Em.FLC)X 1.5 69 266 (Example)
From Table XII it is apparent that assemblies
I to IV all produced similar average contrasts when
exposed between pairs of intensi~ying screens. The
relative lung contrast, reported as 100, was selected
as the contrast corresponding to a density of 1.8,
which is a commonly accepted density for reading lung
featureæ in a radio~raph. Relative heart contr~st was
then fixed as the contrast corresponding to a 1.0 log
E lower exposure level, reflecting the fact that the
heart normally absorbs about 10 times the X-radiation
absorbed by the lungs and therefore allows only about
one tenth of the X-radiation to reach the radiographic
element in the heart image area that reaches the
radiographic element in the lung image areas. While
Assembly I exhibited a lower contrast in its heart
image areas than in its lung image areas, the heart
image area ~or Assembly I was assigned a relative
3~ contrast of 100 for the purpose of comparing contrasts
in the heart image areas of the various assemblies.
In comparing the relative heart area contrasts of
As~emblies II to IV inclusive with that of Assembly I,
it was observed that these latter assemblies provided
only 60 percent of the contrast made available by
Assembly I. The heart area contrasts were
suf~iciently low in the control assemblies as to
~ 5
require ~killed observation to distingui~h ~igni~icant
image features, ~hereas the much larger heart region
relative contrasts provided by Assembly I containing
the double coated radiographic element of the
S invention were clearly di~cernible with much les~
visual effort. A~semblies II, III, and IV demonstrate
that screen manipulation was ineffective in
influencing the contrasts observed using the
conventional extended latitude radiographic element.
Assemblie3 V and VI were included in Table
~II to demonstrate the clear inferior image contrast
observed in heart areas using conventional
xadiographic films of types sometimes used for chest
cavity examinations, but not specifically designed for
this use. With a relative contrast of only 20 in
heart areas, radiographic elements C and D clearly
have limited utility in chest cavity examinations of
heart areas.
It has been demonstrated in related
investigations that double coated radiographic
elements exhibiting crossover levels of les~ than 10
percent and a firæt emulsion layer unit on one side of
a transparent film support that is at lea~t twice,
preferably 2 to lO times, and optimally 2 to 4 times,
the speed of a second emulsion layer unit on the
opposite æide of the support exhibit different average
contrasts when employed in combination with different
screen pair combinations. From these related
investigations it has been concluded that ~ubstitution
of Film A for Film B in either of Assemblies III or IV
would have produced higher average contrasts and, in
all probability, higher contrasts in the heart image
areas.
Assemblies V and VI were constrùcted to
demonstrate that further advantages tha~ can be
realized by combining the teachings of Dicker~on et al
(III) with the teachings of this patent application.
-58-
~ement E (example) (Em.FLC~LXOE(Em.S~C2
Radiographic element ~ was a double coated
radiographic element exhibiting near zero crossover.
Radiographic element E was constructed of a
low crossover support composite (LX0) identical to
that of element A, described above.
Fast low contrast (FLC~ and slow high
contrast (S~C) emulsion layers were coate~ on opposite
sides of the support over the crossover reducing
layers. Both emulsions were green-sensitized high
aspect ratio tabular grain silver bromide emulsions
sensitized and coated similarly as the emulsion layers
of element A.
When coated symmetrically, with Emulsion FLC
coated on both sides of the support and Emulsion SHC
omitted, using a Screen X pair, Emulsion FLC exhibited
a relative log æpeed of 113 and an average contrast of
1.98. Similarly, Emulsion SHC when coated
symmetrically with Emulsion FLC omitted exhibited a
relative log speed of 69 and an average contrast of
2.61. The emulsions thus differed in average contrast
by 0.63 while differing in speed by 44 relative log
speed units (or 0.44 log E).
When Element E was tested for crossover as
described by Abbott et al U.S. Patent 4,425,425, it
e~hibited a crossover of 2%.
Referring to Table ~II, it is apparent that
orienting the Film E with the fast low contrast
emulsion layer adjacent the front screen Z produced
r~sults comparable to that obtained control Film C,
except that a very advantageous doubling of relative
contrast in the heart region was observed. When the
Film E was reveræed, contrast in the lung a~eas was
reduced somcwhat, bu~ remained well within the range
of obt ining useful information ~rom lung image
areas. At the same time relati~e contrast in the
heart region was increased to 266. Thus, this
2~8~
_59_
combination appears superior to all others in Table
XII for obtaining image information from heart areas.
The foregoing compari30ns provide a striking
demon~tration of the advantages which a radiologist
ean realize from the the present invention. The
present invention offeræ the radiologist an improved
diagnostic capability over an extended range of
radiographic element exposures in studying a single
radiographic image.
The invention has been described in detail
with particular reference to preferred embodiments
thereof, but it will be understood that variations and
modifications can be effected within the spirit and
scope of the invention.
